WO2010081423A1

WO2010081423A1 - Conductive film based on graphene and process for preparing the same

Info

Publication number: WO2010081423A1
Application number: PCT/CN2010/070203
Authority: WO
Inventors: 陈永胜; 黄毅; 黄璐
Original assignee: 天津普兰纳米科技有限公司; 南开大学
Priority date: 2009-01-16
Filing date: 2010-01-15
Publication date: 2010-07-22
Also published as: US20120012796A1; CN101474898A

Abstract

Provided is a process for preparing a conductive film, which comprises following steps: 1) coating the surface of a matrix material with a functionalized graphene solution to form a film; and 2) subjecting the film, loaded on the matrix material, obtained by step 1 to chemical reduction and/or calcination. The process can be used to prepare a conductive film on various matrix materials, such as steel, glass, ceramic, quartz, carbon materials, silicon materials, organic materials.

Description

Graphene-based conductive film and preparation method thereof

Technical field

The invention relates to the field of carbon materials, in particular to a graphene-based conductive film and a preparation method thereof. Background technique

Carbon film is a type of film material widely used in the fields of machinery, electronics, construction and medical. At present, the most attractive carbon film materials include diamond film and amorphous carbon film.

In general, both diamond films and amorphous carbon films are prepared by methods such as chemical vapor deposition (CVD) or physical vapor deposition (PVD). In order to grow these two types of films on various substrate materials, these matrix materials must be placed in special instruments, and the substrate materials are required to withstand the arc, plasma, high temperature, high pressure or high required for vapor deposition film formation. Special conditions such as vacuum. Therefore, it is difficult to prepare a carbon film on a substrate material (e.g., a polymer) having poor stability by this method. In addition, limited to the capacity of the instrument cavity, it is difficult to prepare a carbon film on a large-sized or complex-shaped substrate. Summary of the invention

An aspect of the invention provides a method of preparing a conductive film, comprising the steps of:

1) coating a solution containing functionalized graphene on the surface of the substrate to form a film;

2) Chemically reducing the film supported on the substrate obtained in the step 1) and/or another aspect of the invention provides the conductive film obtained by the above method. DRAWINGS

Figure 1 is an optical photograph of a quartz plate coated with a graphene film.

Figure 2 is an optical photograph of a glass sheet coated with a graphene film

Figure 3 is an optical photograph of a polyimide film coated with a graphene film.

4 is an optical photograph of a silicon wafer coated with a graphene film. Detailed description of the invention

Graphene is a new type of two-dimensional nanocarbon material composed of one layer of carbon atoms. The strength of this material is the highest of the known materials. Its electrical conductivity and current carrying density both exceed the best single-walled carbon nanotubes available today. Its excellent Quantum Hall Effect has also been proven. Graphene has received extensive attention due to its excellent electrical conductivity and good physical and chemical stability.

2) chemically reducing the film supported on the substrate obtained in step 1) and/or the term "graphene" as used in the present invention means that the molecular skeleton is composed of carbon atoms arranged by hexagonal lattices. Dimensional planar material, single graphene sheet area of 10 nm ² to 400 μηι ² . The graphene used in the present invention is a single-layer graphene or an oligo-graphene, wherein the thickness of the single-layer graphene is 0.34 nm to 1.4 nm, the number of layers of the oligo-graphene is 2 to 5 layers, and the thickness of the oligo layer is 0.7 nm. To 7 nm

Those skilled in the art will appreciate that the number of layers of oligo-graphene is a statistically significant number of layers. When the number of layers of the oligo-graphene is mentioned to be a certain value or range of values, it does not mean that the oligo-layer graphene contains only the number of layers or the graphene layer of the number of layers. In the present invention, when the number of layers of the oligo-graphene is a certain value or a range of values, the number of layers in the oligo-graphene or the graphene layer in the range of the layer is the oligo-graphene. At least 50%, preferably at least 60%, more preferably at least 70%, still more preferably at least 80% by weight of the total weight.

In a specific embodiment of the invention, the functionalized graphene is prepared by chemical oxidation using graphite as a raw material. The chemically oxidized graphene may have a functional group such as a carboxyl group, a hydroxyl group, an epoxy bond, an ether bond, or a carbonyl group at its edge. The presence of these functional groups imparts a certain water solubility to the graphene so that it can be dissolved or homogenized in water or other aqueous solvent.

In another embodiment of the invention, the functionalized graphene is prepared by reacting chemically oxidized graphene with an organic functionalizing agent. In a particular embodiment, the organofunctionalizing agent used is an isocyanate compound. Different structures of isocyanate compounds react with reactive groups such as hydroxyl groups and carboxyl groups in chemically oxidized graphene, and different in the graphene structure are introduced. The functional group of the machine makes the graphene easy to dissolve or uniformly disperse in the organic solvent.

The isocyanate compounds which can be used in the present invention include, but are not limited to, monoisocyanate compounds and diisocyanate compounds. The monoisocyanate compounds include, but are not limited to, phenyl isocyanate, t-butane isocyanate, cyclohexane isocyanate, hexane isocyanate, cyanophenyl isocyanate, acetylphenyl isocyanate, isocyanatobenzenesulfonic acid azide. The diisocyanate compounds include, but are not limited to, Toluene Diisocyanate (TDI), Methylenediphenyl Diisocyanate (MDI), hexamethylene-1,6-diisocyanate (1,6) -Hexamethylene Diisocyanate, HDI), Isophorone Diisocyanate (IPDI), Hydrogenated Methylenediphenyl Diisocyanate (HMDI).

In a specific embodiment of the present invention, the solvent used in the solution includes water and an organic solvent, wherein the organic solvent includes, but not limited to, acetone, hydrazine, hydrazine-dimercaptoamide (DMF), ethanol, benzene. , dichlorobenzene, tetrahydrofuran and/or acetonitrile.

In a specific embodiment of the invention, the concentration of the functionalized graphene solution is from 0.1 mg/mL to 10 mg/rrLL.

In a particular embodiment of the invention, the method of coating used may include, but is not limited to, soaking, spin coating, spraying or casting.

In a particular embodiment of the invention, the matrix material may be selected from the group consisting of steel, glass, ceramic, quartz, carbon materials, silicon materials, and/or organic materials.

In another specific embodiment, the organic material may be selected from the group consisting of polyurethane, polyacrylate, polyester, polyamide, ABS, polyolefin, polycarbonate, polyvinyl chloride, polyimide, epoxy resin, Phenolic resin and / or rubber.

In a specific embodiment of the invention, when the matrix material is an organic material and the solution containing the functionalized graphene is an aqueous solution, the method further comprises, prior to step 1), activating and enhancing the surface of the organic material. The step of hydrophilicity of the surface of the organic material. In a preferred embodiment of the invention, the activating comprises soaking the matrix material in concentrated sulfuric acid or coating the surface of the matrix material with polystyrene imine and sodium polyphthalate.

In the method for preparing a conductive film of the present invention, the chemical reduction and/or calcination method can completely or partially eliminate the functional groups or defects of the graphene, and restore the structure and properties of the graphene (including conductivity, thermal conductivity and mechanical properties). Wait). In the method of the present invention, the chemical reduction and calcination may be used singly or in combination. In a particular embodiment of the invention, the reducing agent may be selected from the group consisting of hydrazine, hydrazine hydrate, dimethylhydrazine and/or borohydrides such as sodium borohydride and potassium borohydride.

In a particular embodiment of the invention, the chemical reduction is hydrazine hydrate steam fumigation. In a particular embodiment of the invention, the calcination is carried out under vacuum.

In another embodiment of the invention, the calcination is carried out under the protection of an inert gas such as nitrogen, argon or helium.

Another aspect of the invention provides a conductive film obtained by the above method. The conductive film has excellent electrical conductivity and mechanical strength.

Another aspect of the invention provides a method of modifying the surface properties of a substrate material, the method comprising forming a conductive film on the surface of the substrate material by the method of claims 1-14. After the surface is formed into a conductive film, the surface of the base material has excellent electrical conductivity and mechanical strength.

The present invention is specifically described by the following examples, which are only used to further illustrate the present invention, and are not to be construed as limiting the scope of the present invention. Improvements and adjustments are within the scope of the invention. Example 1 : Conductive film based on single layer graphene

The functionalized single layer graphene is prepared by a chemical oxidation process. 10 g of graphite and 7 g of sodium nitrate (analytical grade) were added to the flask, followed by 500 mL of concentrated sulfuric acid (analytical grade). Then, in an ice water bath, 40 g of potassium permanganate was slowly added while stirring, and the addition time was controlled for 2 h, followed by 2 h, and then allowed to cool to room temperature. After stirring at room temperature for 10 days, the reaction solution first changed to green color, and then turned dark brown, and finally became brick brown, and became viscous. The reaction solution was slowly added to 1000 mL of 5 wt% dilute sulfuric acid, and the addition time was controlled for 2 h, and stirring was maintained, and the temperature was controlled at 98. C. The reaction solution was stirred at this temperature for a further 2 h and then cooled to 60. C. Add 30 mL of hydrogen peroxide (30% in water) at 60. C was kept for 2 h, then cooled to room temperature and stirred for 2 h.

In order to remove ions from oxidizing substances, especially manganese ions, impurities in the reaction solution are removed by centrifugation: centrifugation at 4000 rpm for 10 min, the supernatant is removed, and 2 L 3 wt is added to the obtained solid. A mixture of % concentrated sulfuric acid / 0.5 wt% hydrogen peroxide was vigorously stirred and sonicated in a water bath at 200 W for 30 min, and the above operation was repeated 15 times. Thereafter, the above operation was repeated 3 times using 3 wt% of hydrochloric acid, and the above operation was repeated once using distilled water. The reaction solution was then transferred to acetone to remove the remaining acid. Final drying gave a functionalized monolayer of graphene in a yield of 70%. The functionalized single-layer graphene contains an organic functional group such as a hydroxyl group, a carboxyl group, and an epoxy bond, and the mass percentage of the functional group is 20%.

1 g of functionalized monolayer graphene was added to water and sonicated at 500 W for 30 minutes. The dispersion was formed into a film on the surface of the cleaned glass substrate (10×10 cm) by spraying, and left at room temperature for 48 h, and then the glass plate was placed in a pure bismuth solution for 24 h to obtain a reduced single-layer graphene. Conductive film.

The above dispersion of the functionalized single-layer graphene is passed through a spin coating film on a steel plate, an iron plate, a ceramic plate, a quartz plate, an organic film (including polyurethane, polyester, polyamide, ABS, polyethylene, polypropylene). Filming on a base material such as polycarbonate, polyvinyl chloride, polyimide, epoxy resin, phenolic resin or rubber, and obtaining a single layer of graphite supported on different matrix materials by the same reduction method. A conductive film.

The characterization results of the carbon films prepared by this method are shown in Table 1. Table 1

Single layer graphene conductivity matrix material appearance scratch resistance

Carbon film thickness (S/cm) Glass plate 1 μηι Gray, translucent good 5x10 steel plate 1 μηι Gray, translucent good base conductive iron plate 1 μηι Gray, translucent good matrix conductive quartz plate 1 μηι Gray, translucent good 5x10 Ceramic sheet 10 μηι Gray, translucent good 6x10 polyurethane film 10 μηι Gray, translucent good 6x10 polyester film 10 μηι Gray, translucent good 6x10 polyamide film 10 μηι Gray, translucent good 6x10

ABS film 10 μηι Gray, translucent good 6x10 polyethylene film 10 μηι Gray, translucent good 6x10 polypropylene film 10 μηι Gray, translucent good 6x10 PVC film 100 μηι Black, opaque good 6x10 polyimide film 100 μηι Black, opaque good 6x10 epoxy sheet 100 μηι black, opaque good 6x10 Phenolic resin sheet 100 μηι Black, opaque good 6x 10 rubber sheet 100 μηι Black, opaque good 6x 10 Example 2: Transparent conductive film based on single-layer graphene

Functionalized monolayer graphene was prepared as in Example 1. 1 g of the functionalized monolayer graphene was added to water and sonicated at 500 W for 30 minutes to completely disperse.

The above dispersion of the functionalized single-layer graphene was formed into a film on the surface of the cleaned quartz sheet (20 x 20 x 1 mm) by a spin coating film, and left at room temperature for 48 hours. Then, the single-layer graphene film supported on the quartz sheet was placed in a closed container, and steamed with hydrazine hydrate (98%, Alfa Aesar) for 24 hours to obtain a vapor-reduced single-layer graphene film.

A single layer of graphene film reduced by steam was placed in a tube furnace under a nitrogen atmosphere at 400. After calcination at C for 3 h, a transparent conductive single-layer graphene carbon film was obtained.

Alternatively, the vapor-reduced single-layer graphene film is calcined at 1000 ° C for 1 h under vacuum (1 (T ⁵ Torr )) to obtain a transparent conductive single-layer graphene carbon film.

The characterization results of the carbon films prepared by the method of this example are shown in Table 2.

Figure 1 is an optical photograph of a quartz plate coated with a graphene film in which a gray portion is coated with a graphite film, and in order to test its electrical conductivity, a gold electrode is plated with an electrode width and a pitch of 2 mm. Table 2

Example 3: Conductive film based on oligo-layer graphene

5.0 g of graphite and 3.75 g of NaN0 _{3 were} added to a 1 L round bottom three-necked flask, and then 190 ml of concentrated sulfuric acid was slowly poured while stirring. After mixing well, 11.25 g of KMn0 ₄ solid was slowly added, followed by keeping the ice bath for 3 h to bring it to room temperature. After stirring at room temperature for 6 days, slowly to the reaction system Add 500 ml of distilled water dropwise, and at 95~98. The reaction was carried out for 3 hours at C. The reaction solution was cooled, and 15 ml of hydrogen peroxide (30% by weight aqueous solution) was added, followed by stirring at normal temperature. The impurities in the reaction liquid were removed by a centrifugal method similar to that described in Example 1, i.e., an oligographene aqueous solution product was obtained. Further, the solvent water was removed to obtain 2 to 5 layers of the oligo-graphene product.

1 g of the above oligographene graphene was added to water and ultrasonically treated at 500 W for 60 minutes to completely disperse it. Add 0.5 g of sodium borohydride and stir at 80. The reaction was carried out at C for 2 h, and the solution was changed from brown to black to obtain a reduced oligo graphene dispersion.

The above graphene dispersion was formed into a film on the surface of the cleaned glass substrate (10×10 cm) by a casting method, and left at room temperature for 48 hours. The graphene film supported on the glass substrate was then subjected to a nitrogen atmosphere at 400. After calcination at C for 3 h, a conductive oligo-graphene carbon film having a conductivity of 2 x 10 ² S/cm was obtained. Example 4: Material coated with a single-layer graphene-based conductive film

The silicon nitride ceramic was immersed in a single layer of graphene aqueous solution for 10 min, taken out and placed at room temperature for 48 h. It was then placed in a closed container and steamed with hydrazine hydrate (80%, Alfa Aesar) for 24 h. Then under nitrogen protection, at 400. Calcination at C for 2 h gave a silicon nitride ceramic coated with a functionalized single-layer graphene conductive film.

Using the same method, materials such as alumina ceramics, alloy steel, tool steel, pig iron, quartz, glass, silicon wafer, and polyimide film coated with a functionalized single-layer graphene conductive film were prepared. These materials and their characterization are listed in Table 3.

2 is an optical photograph of a glass sheet coated with a graphene film. Fig. 3 is an optical photograph of a polyimide film coated with a graphene film. Figure 4 is an optical photograph of a silicon wafer coated with a graphene film (in order to test its electrical conductivity, a gold electrode was plated with an electrode width and pitch of 2 mm).

Base material coating thickness coating appearance scratch resistance conductivity

( nm ) (S/cm) Silicon Nitride Ceramics 5 Colorless, transparent 2χ 10 ² Alumina Ceramics 5 Colorless, transparent, good matrix conductive Alloy steel 20CrMnSi 4 colorless, transparent good base conductive tool steel SKH52 4 colorless, transparent good base conductive pig iron 4 colorless, transparent good base conductive quartz plate 5 colorless, transparent good 2χ 10 ² glass piece 5 colorless, transparent good 2χ 10 ² Silicon wafer 10 Translucent good 2χ 10 ² Polyimide 10 Translucent good 2χ 10 ² Example 5: Conductive film based on organic soluble single-layer graphene

A single layer of graphene was prepared in accordance with the method of Example 1. 0.2 g of single-layer graphene was placed in a three-necked flask, and 300 mL of distilled DMF was added thereto, and ultrasonically treated at 500 W for 40 minutes to completely disperse. Add 0.4 g of diphenylnonane diisocyanate under nitrogen protection

(Methylenediphenyl Diisocyanate, MDI), and stirred under nitrogen for 5 days at room temperature, then centrifuged at high speed (10,000 rpm) to obtain a solid. The obtained solid was vacuum dried to obtain MDI-functionalized single-layer graphene in a yield of 75%.

Add 0.2 g MDI modified single-layer graphene to 200 mL Ν, Ν-dimercaptoamide

In (DMF), it was sonicated at 500 W for 40 minutes to completely disperse it. Then, a film was formed on the surface of the cleaned glass plate (5 x 5 cm) by a rotary coating method, and left at room temperature for 48 hours. Then, the single-layer graphene film loaded on the glass plate is placed in a closed container, and hydrated with water.

(80%, Alfa Aesar) steam fumigation for 24 h, 肼 steam-reduced MIDI modified single-layer graphene film. The film was then placed in a tube furnace under a nitrogen blanket at 400. Calcination was carried out for 3 h at C to obtain a conductive film based on an organic soluble single-layer graphene. The film has a thickness of 100 nm and an electrical conductivity of 3 x 10 ² S/cm. Example 6: Conductive film based on organic soluble oligo-layer graphene

0.2 g of oligo-graphene was added to a three-necked flask, and 300 mL of steam-filled water-depleted DMF was added, and treated by 500 W ultrasonic (Kunshan Ultrasonic Instrument Co., Ltd., model: KQ-500DB) for 40 minutes to completely disperse. Under a nitrogen atmosphere, 0.3 g of Toluene Diisocyanate (TDI) was added, and the mixture was stirred at room temperature for 5 days under nitrogen atmosphere, and then subjected to high-speed centrifugation (10,000 rpm) to obtain a solid. The resulting solid was dried under vacuum to give TDI functionalized oligographene, yield 70%. 0.2 g of TDI-modified oligo-layer graphene was added to 200 mL of acetone, and treated by 500 W ultrasonic (Kunshan Ultrasonic Instrument Co., Ltd., model: KQ-500DB) for 40 minutes to completely disperse it. The quartz piece (30 x 30 x 3 mm) was then immersed in the acetone dispersion for 10 min, taken out and left at room temperature for 12 h. It was then placed in a closed container and steamed with hydrazine hydrate (80%, Alfa Aesar) for 24 h. Finally, under vacuum (1 (T ⁵ Torr ), calcination at 1100 ° C for 1 h, an oligo-graphene carbon film having a thickness of 10 nm and an electric conductivity of 5 x 10 ⁴ S/cm was obtained. Example 7: Based on Graphene conductive film of polyimide base material

A single layer of graphene was prepared in accordance with the method of Example 1. 2 g of this single layer of graphene was added to water and ultrasonically treated at 500 W for 30 minutes to completely disperse it.

In order to increase the wettability of the polyimide film to water, it is pretreated with a polyelectrolyte solution. 0.5 g of an aqueous solution of polystyrene (molecular weight 70,000) was added thereto, and a 0.5 M aqueous solution of sodium chloride was added thereto to prepare a polystyrene solution having a final volume of 11.1 ml and a concentration of 1.35 mg/ml. A 10 g aqueous solution of sodium polystyrene (molecular weight 100,000) was added, and a certain amount of sodium chloride aqueous solution was added to prepare a polystyrene sodium sulphate solution having a final volume of 66.7 ml and a concentration of 3 mg/ml. The polyimide film was immersed in sodium polystyrene for 20 min, taken out, rinsed with water, and blown dry with a hair dryer. Then, it was immersed in a polyethyleneimine solution for 20 minutes, taken out, rinsed with water, and then blown dry, and the above operation was repeated three times to obtain a polyelectrolyte-modified polyimide film.

The modified polyimide film was immersed in a graphene aqueous solution for 20 min, taken out and left at room temperature for 12 h. It was placed in a closed container and steamed with hydrazine hydrate (80%, Alfa Aesar) for 24 h. Finally, under vacuum (10· ⁵ Torr), at 400. After calcination at C for 1 h, an oligo-graphene carbon film having a thickness of 20 nm and an electric conductivity of 4 x 10 ² S/cm was obtained. Example 8: Graphene conductive film based on polyester matrix material

Graphene was prepared in accordance with the method of Example 3. 2 g of this graphene was added to water and ultrasonically treated at 500 W for 30 minutes to completely disperse it.

In order to increase the wettability of the polyester substrate, the polyester film is first immersed in concentrated sulfuric acid for 10 minutes, and then taken out and rinsed with water to activate the surface of the polyester film.

The polyester film was immersed in the graphene aqueous dispersion for 20 min, taken out and left at room temperature for 12 h, and then the polyester film was placed in a pure bismuth solution for 24 h to obtain a reduced monolayer. Graphene conductive film. It has a thickness of 15 nm and a conductivity of 6X 10- ¹ S/cm. The invention has the following advantages:

1) The single-layer or oligo-layer graphene provided by the invention is soluble in water or an organic solvent, and it is easy to form a uniform carbon film on various materials or objects; compared with conventional chemical meteorological deposition, plasma sputtering, etc. The method has the advantages of simple process, low cost, small equipment investment, and can be applied to products with complicated shapes.

2) Compared with the insulating diamond film and the amorphous carbon film, the graphene-based carbon film has excellent conductivity and graphene has good electrical conductivity and antistatic effect.

3) Graphene has the best mechanical properties of known materials, so that the carbon film provided by the present invention has high strength and modulus, and may be used in special environments such as construction, machinery, and aerospace.

4) Since the graphene has excellent thermal conductivity, the carbon film provided by the present invention has the advantages of easy heat dissipation, and is expected to be applied in the fields of precision instruments and microelectronics.

5) When the thickness of the graphene carbon film is less than 10 nm, it has good light transmittance, and a transparent conductive film can be obtained.

Based on the above advantages, the single-layer or oligo-graphene-based carbon film of the present invention has a good application prospect in the fields of mechanical, construction, medical and other traditional fields as well as high-precision instruments, microelectronics and aerospace.

Claims

Claims:

A method of preparing a conductive film, comprising the steps of:

2) chemically reducing and/or chemically reducing the film supported on the substrate obtained in step 1)

2. The method of claim 1 wherein the functionalized graphene is prepared by chemical oxidation using graphite as a raw material.

3. The method of claim 1 wherein the functionalized graphene is prepared by reacting a chemically oxidized graphene with an organic functionalizing agent, wherein the organofunctionalizing agent used is an isocyanate compound.

4. The method according to claim 3, wherein the isocyanate compound is selected from a monoisocyanate compound or a diisocyanate compound, and the monoisocyanate compound is selected from the group consisting of phenyl isocyanate, t-butane isocyanate, and cyclohexane isocyanate. Hexane isocyanate, cyanophenyl isocyanate, acetyl phenyl isocyanate, isocyanato benzoic acid azide, the diisocyanate compound is selected from the group consisting of decene diisocyanate, diphenyl decane diisocyanate, hexamethylene fluorenyl -1,6-diisocyanate, isophorone diisocyanate, dicyclohexyldecane diisocyanate.

5. The method according to claim 3, wherein the solvent used in the solution is selected from the group consisting of water, acetone, hydrazine, hydrazine-dimercaptoamide (DMF), ethanol, benzene, dichlorobenzene, tetrahydrofuran and/or Acetonitrile.

6. A method according to any of the preceding claims, wherein the concentration of the functionalized graphene solution is from 0.1 mg/mL to 10 mg/mL.

7. A method according to any of the preceding claims, wherein the method of coating used is soaking, spin coating, spraying or casting.

8. A method according to any of the preceding claims, wherein said matrix material is selected from the group consisting of steel, glass, ceramic, quartz, carbon material, silicon material and/or organic material.

9. The method according to claim 8, wherein the organic material is selected from the group consisting of polyurethane, polyacrylate, polyester, polyamide, ABS, polyolefin, polycarbonate, polyvinyl chloride, polyimide, and ring. Oxygen resin, phenolic resin and/or rubber.

10. The method of claim 8 wherein when the substrate material is an organic material and the solution containing the functionalized graphene is an aqueous solution, the method further comprises prior to step 1) The step of activating the surface of the organic material and enhancing the hydrophilicity of the surface of the organic material, the activation preferably immersing the base material in concentrated sulfuric acid or coating the surface of the base material with polystyrene and poly Sodium phenate sulfonate.

A method according to any of the preceding claims, wherein said chemical reduction and said calcination are used singly or in combination.

A method according to any of the preceding claims, wherein the reducing agent used in said chemical reduction is hydrazine, hydrazine hydrate, dihydrazine and/or a borohydride such as sodium borohydride and potassium borohydride.

13. A method according to any of the preceding claims, wherein the chemical reduction is hydrazine hydrazine steam fumigation.

14. A method according to any of the preceding claims, wherein the calcination is carried out under vacuum.

The method according to any one of claims 1 to 13, wherein the calcination is carried out under the protection of an inert gas such as nitrogen, argon or helium.

16. A conductive film produced by the method of any of the preceding claims.

17. A method of modifying the surface properties of a substrate material, the method comprising forming a conductive film on the surface of the substrate material by the method of claims 1-14.